As is known, many pathologies related to the functionality of the spinal column are treated by total or partial immobilization, particularly with a technique known as “intervertebral arthrodesis”, with the aid of connection means and/or with the addition of portions of bone tissue which join such adjacent vertebrae.
Vertebral stabilization devices of the static and dynamic types are known in the art and have a screw that is adapted to be connected to a vertebra, and rigid elements or elements that have a limited mobility and have two ends which are jointly connected to the two screws connected to two adjacent vertebrae.
In particular, a dynamic stabilizing device, i.e., capable of allowing relative movement between the vertebrae, is disclosed in EP 0 669 109. This vertebral stabilizer comprises a spacing body, which is resistant to compression and is adapted to transfer forces between two screws implanted in the respective vertebrae, and a tensioning cord which is connected between the two screws described above and passes in an internal longitudinal cavity obtained in the spacing body.
However, this stabilizer has a drawback, due to the fact that it is directly assembled locally on the spinal column after inserting the screws in the vertebrae, with open surgery in a space that is close to the vertebra. Therefore, the surgical procedure that makes it possible to use such stabilization structure is highly invasive, since it is necessary to create enough space close to the vertebra to perform the various steps of assembly, with considerable difficulty for the surgeon, who has to arrange and assemble each individual element directly on the vertebra.
Moreover, the stabilizer described above does not allow a transverse connection between screws mounted on different vertebrae to transmit forces in a diagonal direction with respect to the axis of the spinal column.
Further, the tensioning cord must be threaded in the spacing body, and this requires a higher skill effort for the surgeon.
Moreover, the surgeon may need a stabilizer that has both static and dynamic portions, i.e., he may have to create a hybrid stabilizer, in which the portions can be chosen by the surgeon according to the characteristics of the pathology.
Known types of stabilizers do not allow creation of a stabilizer of the hybrid type that is totally modular, i.e., capable of adapting to all the configurations that the pathology of the patient may require and are decided on by the surgeon, for example rigid-dynamic-rigid, or dynamic-rigid-dynamic. WO2007/060534, in the name of this same Applicant as the present invention, discloses a vertebral stabilizer of the dynamic modular type, which is adapted to be assembled separately from the spinal column and then fitted onto the spinal column in a few seconds.
However, the known type of stabilizer device is unable to adapt to angle variations with which the pedicle screws might be fitted within the vertebrae, and therefore, if the positioning of such pedicle screws is not performed, in two adjacent vertebrae, with the same angle, the surgeon encounters difficulties in mounting the stabilizer device fitted over the heads of the pedicle screws.